Two areas are under investigation: (1) The structure of the v-sis oncogene is being assayed with respect to its function by means of in vitro mutagenesis. The resulting variants were tested by their ability to transform NIH/3T3 cells in culture using DNA-mediated gene transfer. The structure of the variant protein products was investigated. (2) Using the cloned v-erb B DNA as a probe, we have detected, cloned, and partially characterized a gene similar to but distinct from the EGF receptor gene. This gene is likely to encode a tyrosine kinase protein. Its gene has been found to be amplified in a human mammary carcinoma and thus may have a role in the phenotypic alterations of some human cancers.